My sponge has red spots on it?

It is my first time having a sponge and i don't know why there are spots on it. I only use it for dishwashing and I squeeze it out and dry it once I am done. The spots never show up right away, only after I leave it for a bit to finish drying. Is it safe to use? Is there a way to remove them without damaging... show more It is my first time having a sponge and i don't know why there are spots on it. I only use it for dishwashing and I squeeze it out and dry it once I am done. The spots never show up right away, only after I leave it for a bit to finish drying. Is it safe to use? Is there a way to remove them without damaging the sponge?
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